Avantgarde Acoustic UNO XD Loudspeaker Lab Report

Lab Report

Avantgarde claims an astonishing >107dB sensitivity for the UNO XD but – measuring at 3m and correcting to 1m – we couldn't match that, our pink noise result being 102dB SPL for 2.83V. Bear in mind that Avantgarde's spec. is for 1W input which, given the UNO XD's nominal 18ohm impedance, may represent a higher input voltage. Not that 18ohm fits with our measured minimum modulus of 8.2ohm, which suggests a 10ohm nominal figure. This is still high for a modern loudspeaker nonetheless, and in conjunction with modest impedance phase angles results in a minimum EPDR of 5.6ohm at a high 16.3kHz, making the UNO XD an unusually easy speaker to drive. Not so encouraging about the impedance result is that the modulus vs. frequency and phase vs. frequency traces (not shown) are notably uneven, suggesting the presence of multiple midrange resonances.

Cabinet resonances are dwarfed by a series of modes above 3kHz, presumably from the treble horn

Because of the 3m microphone distance the resolution of the forward frequency response measurements [Graph 1, above] is reduced to about 450Hz and the roll-off below that is an artefact. Not ignorable is the deep but narrow notch at 3kHz, smack on the specified mid/treble crossover frequency, which probably results from imperfect time alignment of the mid and treble horns. (Note that we followed Avantgarde's advice and used a microphone height equal to the mean height of the two horns.) This contributes to very high response errors of ±9.2dB and ±8.6dB, respectively. Pair matching, over the same 500Hz-20kHz frequency range, is also poor at ±3.9dB although the worst disparities are narrowband. The CSD waterfall [Graph 2]can't resolve the midrange resonances but a succession of treble resonances is still clearly visible. KH